Length Frequency Sampling (Part 1 of 2)

Length Frequency Sampling (part 1 of 2) February 11, 2013 Lessen Plan Title: Biological data - Length Frequency Sampling (part 1 of 2) Trainer Name: Training Time: 45 min

Prerequisites:  Manual: chapter 15 (v1.2)  Modules: Random sampling, Fish & Invert ID/anatomy, shark anatomy (measurements)

Audience: West African fisheries observers

Equipment: (include associated file names (e.g. ppt))  AV: LCD projector, computer, laser pointer,  Software: MS Powerpoint, MS Word,  Files: LP_biological_sampling_1.doc, biological_sampling_1.ppt  Props: Nemo (stuffed), measuring tape, length board & strip, calipers  Gear: 9-10 length strips or rulers, pencil, Packets of “fish”, 9-10 ‘baskets’ to put fish in  Activity: Length form exercise

Detailed text associated with ppt presentation) Note: any text in italics is additional information for the trainer and is not intended to be part of the lesson plan. Answers to the questions asked are in orange text. Slide 1 – cover slide

Introduction Biological data, including sex, lengths, weights, and age structures and other specimen, may be collected on a subset of individual fish and invertebrates. This data is used by fisheries stock assessment scientists to estimate the age composition of the population, the length to age ratio, the potential spawning population, the male to female ratio and much more.

The type of length measurement depends on the species being measured. This module will focus on the predominant length types and the generic length form.

Length and other measurements of marine mammals, sea turtles, and seabirds are recorded on separate forms described in Chapter 16 (v1.2) and should not be recorded on the Fish/Invertebrate Length Frequency Form.

Objectives: This module will focus on the common length measurements as well as a brief overview on determining gender. By the end you should be able to…  Explain how length frequency data are utilized.  List the 2 most common measurement types  Describe the primary measurements for various fish and invertebrates  Describe the primary differences between male & female fish and crab  Demonstrate your ability to complete the Fish/Invertebrate Length Frequency Form

1 Length Frequency Sampling (part 1 of 2) February 11, 2013 Slide 4 - Selecting individuals  If you are assigned length sampling, a more detailed species list will be provided prior to deployment. You may need to collect a different number of lengths depending on the species.  Once you know which species and how many of each you need to measure, you will use random sampling techniques to select individuals from your catch composition sample. If you need to measure 10 Butternose from an unsorted haul & there are 100 individuals, what are some methods you might use to choose the 10 fish? [use RNT to select a random number b/w 1 & 10 for random start & select every 10th fish, put all fish in a basket & pour 10 out, split into 6 piles & roll a dice to select pile to measure, etc…] If there are a few more or a few less than the target number of individuals, that’s okay. The most important thing is that they were selected randomly.  How does sorting affect the length sample? [open responses] You may need to take a length sample from both the retained and discarded components. [we need to make some decisions regarding how this type of data can be utilized – you can’t make the same assumptions as with unsorted catch l/fs]  Our protocol states that if you get any individuals that are damaged in a way that the length will not be accurate (e.g., missing tail or rostrum), collect the sex & record them with a length of “0”. However, the LOP may modify this in the future.

Determining gender Because males and females of certain species grow at different rates, fisheries biologists are especially interested in having length frequencies separated by sex so they can better monitor these growth patterns. So, before we get into the length measurements, let’s briefly discuss gender determination. You will also get more practice during the fish lab.

*Gender can be determined using either external or internal characteristics A few species (mostly the cartilaginous fishes) can be sexed based on external features. Male sharks, skates and rays have external claspers emerging from there pelvic fins.

HIDDEN Slide 6 – Determining gender Another example of external sexual dimorphism is the opah. Male opahs have a distinct double edged plate between the head and pelvic fins whereas this area is smoothly rounded in female opahs.

HIDDEN Slide 7 – Determining gender The male dolphinfish has a pronounced bony crest on its ‘forehead’ whereas the female (bottom) forehead slopes gently

Determining gender Most bony fish lack external sexual differentiation features and must be cut open to evaluate internal organs. Gonads are typically located in the posterior portion of the gut cavity near the back bone. The easiest way to access the gonads is to slit the belly 4-8cm parallel to the spine and slightly ahead of the anal opening (vent).

You may need to reach in to move the intestines and fatty tissue aside. Each group of species is slightly different but in general, males have solid gonads that may be smooth or highly crenulated whereas female ovaries are paired sacs. Immature male gonads are frequently string-like. If asked to collect sexed length-frequencies, you will have additional training specific to the species/fishery. If your vessel’s product is whole fish, you may also need to negotiate with the captain to cut open a few fish for the length sample or simply collect unsexed lengths.

2 Length Frequency Sampling (part 1 of 2) February 11, 2013

Determining gender – flatfish Flatfish gonads are also paired, but are located behind the visceral cavity and extend just under the flesh on both sides of the fish, although it is easier to cut on the blind side. Cut back toward the tail from the anus as if skinning the fish. Lift the skin flap and check for a triangular shaped gonad.

Ovaries: Female flatfishes have elongate triangle-shaped ovaries that extend from behind the anal spine area almost to the tail when mature. When immature, the ovaries will be almost equilateral triangles with one angle shaped like a smoothly rounded tube extending only slightly back toward the tail (the triangle looks like a funnel in shape). The color will be pink or orange. Ovaries always have rounded edges.

Testes: Male flatfishes have a white, equilateral triangle-shaped gonad on each side. The triangle will not have a tail extending back toward the caudal fin. Immature males have a small crescent moon shaped, tan colored gonad laying right at or behind the anal spine location. All male flatfishes have “edges” to the triangle. If you lift the gonad with the knife or scalpel and examine the sides of the triangle, you can distinguish the sharp edges (male) or rounded sides (female), even on an immature flatfish.

HIDDEN Slide 10– Determining gender – invertebrates - shrimp Determining gender of invertebrates varies by group. For shrimp, the difference is on the first pair of swimming legs (pleopods). Male endopods are notched and if mature will have a petasma which is essentially an organ that attaches a sperm packet. Female endopods are pointed and unmodified. You will not need to separate shrimp by sex unless specifically assigned a special project.

Determining gender – invertebrates - crab For crab, the main difference between the sexes is the shape of the abdominal flap. Females tend to have larger, rounder flaps whereas males are smaller and more triangular in shape. Sometimes the differences are obvious.

Determining gender – invertebrates – crab However, there is a lot of variation among the species and a few species the differences between male and female are not that great (as shown in this photo).

HIDDEN Slide 13– Determining gender – invertebrates – lobster The primary difference between male and female lobsters is the size of the first pair of swimmerets: females are thin and filament-like whereas males are thick in shape and firm in texture. Females also have a relatively large genital opening (seminal receptacle) that extends between the third and fourth pair of walking legs whereas males have very small genital openings at the base of the fifth pair of walking legs.

Measuring lengths - fish In general, fish measurements are taken along the longest longitudinal axis. Straight-line measurements are preferred to measurements over the curve of the body. The most common measurements used for fish are fork length and total length. You may be asked to take a curvilinear measurement on some very large billfish or turtles. The curvilinear measurement is along the curve of the fish. [use stuffed Nemo

3 Length Frequency Sampling (part 1 of 2) February 11, 2013 as teaching aid]. Which length is longer? [curvilinear] There are many other length types explained more thoroughly in Table 15-1.

Length measurements will be rounded down to the nearest whole centimeter (fish) or millimeter (invertebrates). For instance, this fish would be recorded as 20 cm if we were taking fork length or 21 if we were recording total length.

Measuring lengths A few measuring tips include:  You should close the mouth and straighten the fish so you can measure its full length. Sometimes this is challenging because the fish are still alive & squirming. Be patient.  The snout should be resting gently against the head piece of the measuring board or other vertical surface.  Always be sure to keep your eye directly above the tail of the fish to ensure the correct measurement is recorded. If the measurement is taken when your eye is not directly above the tail of the fish, the measurement will be read at an angle, possibly giving an incorrect result.  When an individual is larger than the measuring device provided, measure it by taking two or more measurements.

Measuring lengths The fork length is measured from the tip of the snout to the center of the fork in the tail. This is most common on species with concave or forked tails. If the arrow indicates 10cm, what is the fork length of the fish in the photo? [15 cm]

Measuring lengths The total length you will most often measure is the distance between the tip of the snout to furthest tip of tail in the natural position. Typically taken on species with convex tails. If we assume the snout is pressed up to the yellow box, what is the total length of the fish in this photo ? [16 cm]

Measuring lengths – Sharks Maximum (also pinched or stretched) total length is measured from the snout to tip of tail flexed down to center line like the fish tail shown here.

Measuring lengths – Sharks The primary measurement for most sharks is the stretched total length.

Measuring lengths - damaged What do you do if you get a fish that’s damaged in some way like this one without a tail? [Record length as zero (0) next to appropriate sex.]

Measuring lengths ▸ Disc length (pelvic) –Tip of the snout to the posterior edge of the pelvic fins ▸ Typical measurement for Myliobatoidei

HIDDEN Slide 22 Measuring lengths

4 Length Frequency Sampling (part 1 of 2) February 11, 2013 The disc width is the distance between the furthest opposite points of the wings on batoid type fish. This is a secondary measurement for skates & rays

Measuring lengths - Inverts The most common measurements used for invertebrates are total length, carapace length and carapace width. More definitions can be found in Table 15-4 in the manual.

(Note that there are a variety of total length definitions but the preferred definition for shrimp is from the tip of the rostrum to the posterior tip of the telson (code 31).

uropods The tail end of a shrimp has 2 features that could be confusing. There are 2 pairs of uropods and 1 telson (center).

Measuring lengths - Inverts For crab & lobster, the carapace length is defined as the posterior edge of the eye socket to median posterior carapace.

Measuring lengths - Inverts Carapace width is the largest width across the carapace including marginal spines (crab). This is the preferred measurement for crab

Length frequency form Complete a Fish/Invertebrate Length Frequency Form for each sampled haul where length measurements of fish or invertebrates were collected. Multiple species can be recorded on each page.

The top of the form has the standard identifying information – observer code, vessel code, trip ID, date & haul number.

*Next, record the common or scientific name of the species as well as the appropriate 3-letter species code from Appendix 7.

IRecord M, F, I or U for Male, Female, Indeterminate or Unknown. What is the difference between Indeterminate and Unknown? Record Indeterminate when you inspect gonads but are unsure of sex and unknown when gonads are not inspected.

Maturity field For fish & male crab and lobster, leave maturity column blank for now. This field may be added to sampling protocol at a later date. If you measure female crab or lobster, you should also assess maturity which is based on the presence or absence of eggs and whether or not the eggs have visible eyes. How would you classify the specimen in the photo? [mat=3]

Length frequency form Record the length type for each species that you measured. The common codes are listed at the bottom of the form and a more detailed list appears in your manual. *Length type is a combination of the number and letter (e.g. 01S).

6 Length Frequency Sampling (part 1 of 2) February 11, 2013 Slide 30 Length frequency form Record each length and the count of each length encountered in ascending order. *Record the count of unmeasureable individuals for each species as length=0.

*Sum the lengths and counts for each row and record the sum in the KPC column. The Key punch check will be used as a quality control check during data entry.

*There is also space at the bottom of the page for comments regarding unusual observations or sampling difficulties.

Activity (instructions & staff needs):  Groups of 3  Each packet of ~80 “fish” has information on the species, length type, and target number of fish to measure  Each “fish” has a sex recorded on it ♀ or ♂  Make a sampling plan before making any measurements  Measure a subsample of fish according to your plan. Explain how to use length-frequency strip  Complete Fish/Invertebrate Length Frequency form and questions on the handout  15 minutes

Slides 32-34 Summary or summary questions: Review the main objectives ▸ How are length frequency data utilized? [estimate the age composition of the population, the length to age ratio, the potential spawning population, the male to female ratio, etc.] ▸ What are the most common measurement types for ▸ bony fish with a round tail? [total length] ▸ crab? [carapace width] ▸ skates/rays (not Myliobatoidei)? [total length] ▸ Sharks without distinct fork) [maximum or stretched total length] ▸ What are the primary differences between male & female fish [open] ▸ What are the crab genders? [clockwise from left: 1-Male, 2-male, 3-female ] ▸ How would you record the maturity of these gravid crab? [1. Maturity code 4 (eggs visible – eyes unknown); 2. Maturity code =3 (eggs visible, eyes visible)]

7 Length Frequency Sampling (part 1 of 2) February 11, 2013 Activity - Fish/Invertebrate Length Frequency Sample

Names:

Observer code: A732; Vessel code: LIB732; Trip 91; Date: May 1, 2011; haul 3

Which species did you measure?

What was the population for your length frequency sample?

How many fish were you targeting to measure?

How did you select individual fish?

How would you describe your sampling frame (spatial, temporal, other)?

Describe any factors that may have affected your random sample:

9 Length Frequency Sampling (part 1 of 2) February 11, 2013 Activity - Fish/Invertebrate Length Frequency Sample [Answer Key – Total points = 12]

Names:

Observer code: A732; Vessel code: LIB732; Trip 91; Date: May 1, 2011; haul 3

1 Which species did you measure? Options include:  CVJ – Caranx hippos  PET – Capitan Royal  BOA – Ethmalosa fimbriata  ILI – Illisha africana

1 What was the population for your length frequency sample? ~80 fish

1 How many fish were you targeting to measure? 16 (80*0.2) or 12 (80 * 0.15) – This should also be close to the actual number measured but there may be some variation around 16 or 12.

How did you select individual fish? 1 Response should be a description that includes how they selected the 12 or 16 fish out of the 80. It should include how random numbers were selected and how that was applied to selecting the fish to measure.

1 How would you describe your sampling frame (spatial, temporal, other)?

Spatial – temporal may be an option but not likely given the training thus far

0 Describe any factors that may have affected the randomness of this length sample:

This is a freeform answer – As long as it makes sense it’s okay.